Proton structure at the LHC
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Date
27/11/2014Author
Hartland, Nathan Philip
Metadata
Abstract
A determination of Parton Distribution Functions (PDFs) from a global fit to
a dataset including measurements from the LHC has been performed for the
first time. The determinations have been performed according to the NNPDF
methodology, leading to a fit relatively free of parametrisation bias and with an
accurate account of PDF uncertainty.
In this thesis the importance of QCD measurements at the LHC to PDF
extraction are discussed, and we summarise some of the technical difficulties in
their inclusion into PDF fits. A number of methods are presented that permit
the efficient inclusion of these observables into PDF determinations.
Firstly a Bayesian reweighting procedure taking advantage of the Monte Carlo
representation of PDF uncertainties in NNPDF sets is discussed. The utility of
the Bayesian reweighting method is demonstrated by a study of the impact of
early W production asymmetry measurements from ATLAS, CMS and LHCb
upon an earlier PDF set.
A package for the fast computation of observables in an automated NLO
framework is presented, providing an interface between Monte Carlo event
generators and NLO interpolation tools.
Finally, a new method of combining PDF evolution with interpolating codes
for hadronic observable computation is also described. This method largely
overcomes the computational difficulties in performing fast perturbative QCD
predictions for collider observables. The method has been applied to the
determination of PDFs from a global dataset including electroweak vector boson
production data from LHCb, ATLAS and CMS along with inclusive jet data from
ATLAS. The resulting set, NNPDF2.3 provides the most accurate determination
of parton distributions via the NNPDF methodology to date.
Finally, the method of closure testing is introduced, and the method is applied
to the study of the NNPDF methodology. A number of improvements are found in
the minimisation and stopping procedures, which are adopted for the development
of the next NNPDF release, NNPDF3.0. Alongside the sounder methodological
basis, the NNPDF3.0 PDF set will provide a determination based upon an
expanded datfits.